While most wells are drilled more or less vertically, it is not uncommon to deviate a well so that it is drilled at an angle from the vertical. A typical situation arises with an offshore platform where many wells are brought to the surface at the platform. It is not uncommon to find as many as thirty wells at a single platform. While several of the wells might deviate only a few degrees from the vertical, a large number of such wells will deviate outwardly from the platform to place a number of wells into a productive formation. Of the thirty wells, perhaps as many as twenty will be substantially deviated from the vertical. They will typically radiate in all directions of the compass on viewing the platform from above. The angle of deviation in a given well will vary significantly. Deviation angles in the range of zero to about 45 degrees still permit the use of wireline supported equipment in the drilling of the well, and various and sundry completion techniques. When a well is highly deviated, typically in the range of about 45 to about 75 degrees, it is more appropriate to describe the well as being horizontal than vertical, at least in the deviated portion. Such high angles of deviation from the vertical create more or less horizontal portions in the well, and there are difficulties in getting wireline tools through such highly deviated portions.
Wireline supported tools, whether supported on a slick line or on a multi-conductor armored logging cable, including a support wire and various conductors, all operate successfully by traversing the well borehole by gravity. Gravity fall and wireline retrieval is thus a routine matter in getting wireline supported tools into and out of the well borehole. In a highly deviated well, the wireline supported tools do not travel so readily.
In a highly deviated hole, wireline tools may snag or hang on the rough surface that defines the drilled hole. In open hole, the surface can vary over a wide range of roughness. Even when it is smoothed by a mud cake there still is a high risk of snagging the gravity moved wireline tool. Even if the hole has been cased, there is still an element of risk of snagging the tool at threaded connections between joints.
One approach to overcoming the possibility of snagging in highly deviated holes is to run the logging tool into the well on a string of drill pipe. This is described as being "drill pipe conveyed". An assembly is connected to the lower end of a string of drill pipe and is forced into the deviated hole to position the logging apparatus at a specified depth in the hole. When this is done, positioning can be achieved in a reliable fashion, but it is then difficult to get the signals created by the logging apparatus out of the well. For instance, logging apparatus supported by a string of drill pipe may form a multitude of signals transmitted from the logging apparatus up through the drill string. Heretofore, signals have been delivered by means of various conductors in an armored logging cable. While the drill pipe is made of metal and can serve as a pipe conductor, in practice, quality of the conductor is so poor that an electrical connection must be made with a high quality conductor wire, one pair or more, to thereby provide a signal path. Moreover, some logging tools utilize electrical power and thus, a quality connection must be made from the surface to the logging tool (on the drill string) whereby electric current flows from the surface to the logging apparatus. The required quality of connection mandates the use of a logging cable including at least a pair of conductors to deliver electric current from the surface to the logging apparatus, and also, the incorporation of suitable conductor paths to deliver signals from the logging apparatus back to the surface. This can be done with a pair of conductors, if nothing else through the use of multiplexing to obtain the equivalent of more than a single conductor pair.
With this background in mind, the present disclosure is directed to a system whereby a logging tool in the form of an assembly affixed to a string of drill pipe is first installed at a suitable depth in the well. Thereafter, an overshot is dropped into the string of drill pipe. If it tends to stall, it can be pumped down by the use of a drilling fluid such as drilling mud. This will force it to the bottom. At that point, the overshot makes mechanical and electrical connection to the logging assembly for the purpose of providing the quality electrical connection required for operation. The present apparatus enables a connection to be made, disclosing a pumpdown overshot cooperative with a wet connector. Moreover, it enables mechanical connection utilizing a type of self-cleaning boot with a bayonet connector featuring a J-slot which enables a positive mechanical connection to be made. it is not sensitive to dynamic pressure which may vary widely depending upon circumstances of the deviated well. Connection is achieved wherein the mechanical load is handled separately, in a manner of speaking, so that separate and proper electrical connection is achieved. The overshot latches to the wet connector assembly at the bottom of the string of drill pipe, thereby assuring proper operation of the system. By proper manipulation of wireline tension, connection can be made and then connection can be ended enabling retrieval of the wireline and the overshot affixed to it.
While the foregoing sets forth the problem and mentions briefly certain features of the present apparatus, the detailed description set forth below will more clearly describe the construction of the apparatus and its mode of operation.